Manual placement of SD‐OCT peripapillary circle scan: possible influence on RNFLT classification and profile shape

Purpose Automatic classification of peripapillary retinal nerve fiber layer thickness (RNFLT) with Spectral Domain OCT (SD‐OCT) using a circle scan centered at the optic nerve head (ONH) is a standard test in glaucoma diagnosis. Possible influences of manual center selection on the double‐hump (DH) shape of RNFLT profile and classification have been evaluated. Methods SD‐OCT (Spectralis , Heidelberg Engineering GmbH, Germany) standard circle scans were performed on 17 healthy eyes. Based on the infrared (IR) reflectance image, the center (C) of the circle scan was manually aligned to the ONH center and then shifted half way to the rim and on the rim at 3, 6, 9 and 12 o’clock position. Angle (AHP) and thickness (THP) of the highest peak in the superior and inferior RNFLT profile were calculated. Changes in RNFLT classification were analyzed. Results Horizontal shift of C significantly affects the AHP. Temporal shift moves the DH together, nasal shift diverges it. Temporal or nasal shift results in higher changes of superior than inferior RNFLT profile. Vertical shift induces a significant difference between THP and AHP. Superior shift increases inferior THP, decreases superior THP and moves the DH slightly to the left. Inferior shift does the opposite. The first temporal shift changed normal RNFLT classification in 15 of 119 sectors: 10 borderline (BL), 5 outside normal limits (ONL). Shifting C further on the temporal rim changed 33 sectors: 9 to BL, 24 to ONL. Conclusion Extreme decentration of the circle scan center (C) can significantly affect position and height of the RNFLT profile double hump (DH). If the RNFLT DH profile does not match the typical normal shape, decentration of C should be considered as a possible reason.Commercial interest